Fix broken compilation of uClibc-ng.

During buildroot compilation with latest uClibc
I've encoutered linking error due to multiple definition
of some symbols from DNS code.
The error happens because the same file resolv.c
is included inside many other .c files:
res_comp.c:(.text+0x0): multiple definition of `__GI___dn_expand'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0x8a0): first defined here
res_comp.c:(.text+0x0): multiple definition of `__dn_expand'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0x8a0): first defined here
res_comp.c:(.text+0x34): multiple definition of `__GI___dn_comp'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0xc68): first defined here
res_comp.c:(.text+0x34): multiple definition of `__dn_comp'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0xc68): first defined here
ns_name.c:(.text+0x4c): multiple definition of `__GI___ns_name_ntop'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0x4c): first defined here
ns_name.c:(.text+0x4c): multiple definition of `__ns_name_ntop'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0x4c): first defined here
ns_name.c:(.text+0x1f8): multiple definition of `__GI___ns_name_pton'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0x1f8): first defined here
ns_name.c:(.text+0x1f8): multiple definition of `__ns_name_pton'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0x1f8): first defined here
ns_name.c:(.text+0x624): multiple definition of `__hnbad'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0x624): first defined here
ns_name.c:(.text+0x718): multiple definition of `__GI___ns_name_unpack'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0x718): first defined here
ns_name.c:(.text+0x718): multiple definition of `__ns_name_unpack'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0x718): first defined here
ns_name.c:(.text+0x84c): multiple definition of `__GI___ns_name_uncompress'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0x84c): first defined here
ns_name.c:(.text+0x84c): multiple definition of `__ns_name_uncompress'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0x84c): first defined here
ns_name.c:(.text+0x8a0): multiple definition of `__GI___ns_name_pack'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0x8d4): first defined here
ns_name.c:(.text+0x8a0): multiple definition of `__ns_name_pack'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0x8d4): first defined here
ns_name.c:(.text+0xbe4): multiple definition of `__GI___ns_name_compress'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0xc18): first defined here
ns_name.c:(.text+0xbe4): multiple definition of `__ns_name_compress'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0xc18): first defined here
ns_name.c:(.text+0xc34): multiple definition of `__GI___ns_name_skip'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0xcdc): first defined here
ns_name.c:(.text+0xc34): multiple definition of `__ns_name_skip'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0xcdc): first defined here
ns_name.c:(.text+0xcd4): multiple definition of `__GI___dn_skipname'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0xd7c): first defined here
ns_name.c:(.text+0xcd4): multiple definition of `__dn_skipname'; libc/libc_so.a(encodeq.os):encodeq.c:(.text+0xd7c): first defined here
My previous commit that fixes build error of DNS code is okay,
but there are some 'bottlenecks' in uClibc-ng code, so if
we don't want to completely rewrite resolv.c we need to make some
symbols weak to prevent linking errors.

libc/inet/resolv.c

@@ -2809,7 +2809,7 @@ libc_hidden_def(gethostbyaddr)
  * 'exp_dn' is a pointer to a buffer of size 'length' for the result.
  * Return size of compressed name or -1 if there was an error.
  */
-int dn_expand(const u_char *msg, const u_char *eom, const u_char *src,
+int weak_function dn_expand(const u_char *msg, const u_char *eom, const u_char *src,
 				char *dst, int dstsiz)
 {
 	int n = ns_name_uncompress(msg, eom, src, dst, (size_t)dstsiz);
@@ -2818,14 +2818,14 @@ int dn_expand(const u_char *msg, const u_char *eom, const u_char *src,
 		dst[0] = '\0';
 	return n;
 }
-libc_hidden_def(dn_expand)
+libc_hidden_weak(dn_expand)
 
 /*
  * Pack domain name 'exp_dn' in presentation form into 'comp_dn'.
  * Return the size of the compressed name or -1.
  * 'length' is the size of the array pointed to by 'comp_dn'.
  */
-int
+int weak_function
 dn_comp(const char *src, u_char *dst, int dstsiz,
 		u_char **dnptrs, u_char **lastdnptr)
 {
@@ -2833,7 +2833,7 @@ dn_comp(const char *src, u_char *dst, int dstsiz,
 			(const u_char **) dnptrs,
 			(const u_char **) lastdnptr);
 }
-libc_hidden_def(dn_comp)
+libc_hidden_weak(dn_comp)
 #endif /* L_res_comp */
 
 
@@ -2873,7 +2873,7 @@ static int special(int ch)
  * note:
  *      Root domain returns as "." not "".
  */
-int ns_name_uncompress(const u_char *msg, const u_char *eom,
+int weak_function ns_name_uncompress(const u_char *msg, const u_char *eom,
 		const u_char *src, char *dst, size_t dstsiz)
 {
 	u_char tmp[NS_MAXCDNAME];
@@ -2886,7 +2886,7 @@ int ns_name_uncompress(const u_char *msg, const u_char *eom,
 		return -1;
 	return n;
 }
-libc_hidden_def(ns_name_uncompress)
+libc_hidden_weak(ns_name_uncompress)
 
 /*
  * ns_name_ntop(src, dst, dstsiz)
@@ -2897,7 +2897,7 @@ libc_hidden_def(ns_name_uncompress)
  *      The root is returned as "."
  *      All other domains are returned in non absolute form
  */
-int ns_name_ntop(const u_char *src, char *dst, size_t dstsiz)
+int weak_function ns_name_ntop(const u_char *src, char *dst, size_t dstsiz)
 {
 	const u_char *cp;
 	char *dn, *eom;
@@ -2967,7 +2967,7 @@ int ns_name_ntop(const u_char *src, char *dst, size_t dstsiz)
 	*dn++ = '\0';
 	return (dn - dst);
 }
-libc_hidden_def(ns_name_ntop)
+libc_hidden_weak(ns_name_ntop)
 
 static int encode_bitstring(const char **bp, const char *end,
 							unsigned char **labelp,
@@ -3081,7 +3081,7 @@ static int encode_bitstring(const char **bp, const char *end,
 	return 0;
 }
 
-int ns_name_pton(const char *src, u_char *dst, size_t dstsiz)
+int weak_function ns_name_pton(const char *src, u_char *dst, size_t dstsiz)
 {
 	static const char digits[] = "0123456789";
 	u_char *label, *bp, *eom;
@@ -3202,7 +3202,7 @@ int ns_name_pton(const char *src, u_char *dst, size_t dstsiz)
 	errno = EMSGSIZE;
 	return -1;
 }
-libc_hidden_def(ns_name_pton)
+libc_hidden_weak(ns_name_pton)
 
 /*
  * __hnbad(dotted)
@@ -3218,7 +3218,7 @@ libc_hidden_def(ns_name_pton)
  * return:
  *	0 if the name is ok
  */
-int __hnbad(const char *dotted)
+int weak_function __hnbad(const char *dotted)
 {
 	unsigned char c, n, *cp;
 	unsigned char buf[NS_MAXCDNAME];
@@ -3255,7 +3255,7 @@ int __hnbad(const char *dotted)
  * return:
  *      -1 if it fails, or consumed octets if it succeeds.
  */
-int ns_name_unpack(const u_char *msg, const u_char *eom, const u_char *src,
+int weak_function ns_name_unpack(const u_char *msg, const u_char *eom, const u_char *src,
                u_char *dst, size_t dstsiz)
 {
 	const u_char *srcp, *dstlim;
@@ -3322,7 +3322,7 @@ int ns_name_unpack(const u_char *msg, const u_char *eom, const u_char *src,
 		len = srcp - src;
 	return len;
 }
-libc_hidden_def(ns_name_unpack)
+libc_hidden_weak(ns_name_unpack)
 
 static int labellen(const unsigned char *lp)
 {
@@ -3416,7 +3416,7 @@ next:
 	return -1;
 }
 
-int ns_name_pack(const unsigned char *src,
+int weak_function ns_name_pack(const unsigned char *src,
 				 unsigned char *dst, int dstsiz,
 				 const unsigned char **dnptrs,
 				 const unsigned char **lastdnptr)
@@ -3525,9 +3525,9 @@ cleanup:
 
 	return dstp - dst;
 }
-libc_hidden_def(ns_name_pack)
+libc_hidden_weak(ns_name_pack)
 
-int ns_name_compress(const char *src,
+int weak_function ns_name_compress(const char *src,
 					 unsigned char *dst, size_t dstsiz,
 					 const unsigned char **dnptrs,
 					 const unsigned char **lastdnptr)
@@ -3539,9 +3539,9 @@ int ns_name_compress(const char *src,
 
 	return ns_name_pack(tmp, dst, dstsiz, dnptrs, lastdnptr);
 }
-libc_hidden_def(ns_name_compress)
+libc_hidden_weak(ns_name_compress)
 
-int ns_name_skip(const unsigned char **ptrptr,
+int weak_function ns_name_skip(const unsigned char **ptrptr,
 				 const unsigned char *eom)
 {
 	const unsigned char *cp;
@@ -3583,9 +3583,9 @@ int ns_name_skip(const unsigned char **ptrptr,
 
 	return 0;
 }
-libc_hidden_def(ns_name_skip)
+libc_hidden_weak(ns_name_skip)
 
-int dn_skipname(const unsigned char *ptr, const unsigned char *eom)
+int weak_function dn_skipname(const unsigned char *ptr, const unsigned char *eom)
 {
 	const unsigned char *saveptr = ptr;
 
@@ -3594,7 +3594,7 @@ int dn_skipname(const unsigned char *ptr, const unsigned char *eom)
 
 	return ptr - saveptr;
 }
-libc_hidden_def(dn_skipname)
+libc_hidden_weak(dn_skipname)
 #endif /* L_ns_name */